Reaction injection polyurethane moldings have been increasingly used in the manufacture of automobiles, furniture, industrial service parts and in home construction. The high demand for molded polyurethane articles has required that they be produced in the large numbers and having the shortest possible gel times. However, providing an adequate mold release with the shortest possible gel time has continued to be a problem which has plaqued the industry.
Previously, to facilitate the release of molded polyurethane articles from the molds in which they are formed, three methods were utilized: the mold cavity was coated with a mold release agent ("external mold release agent"); a mold release agent was included in the polyurethane forming reaction mixture ("internal mold release agent"); or the polyurethane itself was coated directly with a mold release agent ("resin coating mold release agent").
However, many problems exist with the conventional prior art techniques particularly when the RIM process is utilized. The RIM process is characterized as a combination of high pressure impingement mixing and the rapid injection of liquid resins into molds where the polyurethane-forming materials meet, react and cure rapidly. It is generally believed that mold release, using an internal mold release agent, is inherently unattainable because of the short gel times of certain urethane formulations which would not allow the internal release agent molecules to migrate to the mold-polyurethane interface.
External mold release agents usually consist of natural or synthetic compounds, such as silicone oils, mineral oils, waxes, fatty acid derivatives, glycols, etc. Generally, these release agents are either dissolved or dispersed in a liquid carrier and are sprayed into the mold cavity. Such known external release agents have a short working lifetime which therefore necessitates reapplication of the release agents to the mold prior to each molding cycle. This reapplication of the release agent after each molding cycle or a limited number of molding. cycles interrupts the molding operation and slows down output. This method of application inherently results in "thick" (by molecular standards), weak layers of the release agent on the mold surface. These layers can break randomly during demolding and leave residues of the release agent on both the mold and the molded articles.
More importantly, conventional wax and soap external release agents are generally not suitable for the RIM process. The combination of high pressure impingement mixing and the rapid injection of the liquid resins into the mold push the conventional wax release and soap release agents off the mold surface or redistribute them unevenly on the mold surface. This results in a non-uniform layer of the external release agent on the mold surface which can not only affect the shape of the molded article but make release (in the areas not containing the release agent) difficult, if not impossible.
Certain DuPont literature discloses the use of "Zonyl" compounds (e.g. FSP, FSA, etc.) as mold release agents for plastics. However, this trade literature does not contain any teachings or methods for the specific use of these compounds. Other DuPont trade literature published August, 1982, makes no reference to any mold release use of "Zonyl" compounds.
U.S. Ser. No. 509,134, "Monolayer Mold Release", filed June 29, 1983 discloses an external mold release method for imparting monolayer mold release properties to molded polymeric materials. This method is especially useful in the RIM process since the monolayer mold release agent is actually adsorbed onto the metal molding surface. This adsorption or actual bonding of the monolayer mold release agent to the metal surface can also prevent problems normally associated with mold release in the RIM process. Monolayer mold release agents include the following: perfluoroalkylorganocarboxylic acids or salts thereof; alkyl carboxylic acids or salts thereof; perfluoroalkyl group-containing phosphoric acid esters or salts thereof; or alkyl phosphoric acids or salts thereof.
U.S. Pat. No. 3,726,952 discloses the use of internal mold release agents containing at least 25 carbon atoms that are salts of an aliphatic carboxylic acid and either a primary amine or amine containing amide or ester groups. While these additives do impart some release properties, these additives contain fatty acid groups which can interfere with the curing of the urethane foam formulation.
Other internal mold release agents are described in U.S. Pat. No. 4,118,235 (Horiuchi, et al) which discloses the use of a perfluoroalkyl group-containing phosphoric acid ester and an additive consisting of either a highly fluorinated organic compound, a wax or a mixture thereof. Horiuchi, et al discloses that "the mixture of the surface active agent (additive) and the perfluoroalkyl phosphoric acid ester exhibit, . . . releasing ability far superior to that attained by the perfluoroalkyl group-containing phosphoric acid ester alone." (Column 3, lines 64-48). Horiuchi also discloses that, at the low concentrations of additive used, it would be impossible to use the ester alone (Column 4, lines 1-4). Japanese Pat. Nos. 78/40,042 and 80/133,490 are both similar to Horiuchi et al. These two Japanese patents as well as Horiuchi et al teach that the phosphoric acid ester containing a perfluoroalkyl group, when used alone, is inadequate in achieving multiple releases, but improved release properties can be obtained when the claimed perfluoroalkylphosphoric acid ester is used in combination with at least one release agent.
U.S. Pat. No. 4,111,861 claims four classes of internal mold release agents or additives. Most pertinent are additives which consist of mixtures of fatty acids and metal salts or metal alkyl carboxylates. These aliphatic and aryl carboxylic acids lack a perfluoralkylorgano moiety.
Finally, a "resin coating mold release agent" is disclosed in U.S. Pat. No. 4,331,764 (Franz). Franz discloses providing a resin coating mold release agent by forming a lubricating, nonreactive species at the polyurethane surface. Preferably, a "carboxylated fluorosurfactant" is chemisorbed at the polyurethane surface to produce a substantially monomolecular layer of the fluorosurfactant which is lubricating and nonreactive. In the Franz process, the preferred nonreactive species include carboxylated fluorosurfactants, particularly anionic "moderately carboxylated" fluorosurfactants. The particular mold release agent disclosed in Example I of Franz, ("Zonyl FSP") is disclosed in the above-mentioned DuPont trade literature as being a phosphate ester and not a "carboxylated fluorosurfactant" (which is the generic term used by Franz to describe Franz' release agents). Furthermore, in Franz' Example II, the surface of the press is treated with siloxane (and not with any fluorosurfactant) prior to contacting the press with a polyurethane containing the Franz' release agent. No particular treatment of the polyurethane surface is disclosed by Franz prior to the application of Franz' release agent.
It is an object of the present invention to provide a polyurethane composition which exhibits internal mold release properties upon the addition of a perfluoroalkylorganocarboxylic acid or salt thereof.
It is an object of the present invention to provide novel tin compound-containing polyurethane compositions which not only exhibit internal mold release properties, but are also inherently catalytic.
Various other objects and advantages of this invention will become apparent to those skilled in the art from the accompanying disclosure and description.